Works. Here's what I replaced your code with:
$msg = 'No Facebook association was found. Would you like to register?';
$app->redirect(JRoute::_('index.php?option=com_xipt&view=registration', false), $msg);
This makes it very non-confusing for the user
Now, of course, there's no Facebook profile being brought down, but that's okay. They can associate later. So in cases where a site admin has XIPT loaded, this removes any bifurcation of the registration flow.
Now... another thing you'll want is an option in SCLogin for XIPT that goes to the route, above. Right now, my XIPT goes to JomSocial, but if you added XIPT as an option, it would go there directly and avoid an extra plugin trap and redirection.
The *real* fun will be in integrating Facebook signup with XIPT. This is because XIPT does all kinds of field manipulation based on profiletype. This might make it tough for you to fill in the fields with Facebook values. I suspect you'll need *them* to consume your data, once set. That's going to be some discussion between you and them, I think.
Again, though, they say they may have done this work in PayPlans. I'll know in a few days when I purchase and integrate that to see what it does.
But for now, this gets me what I needed and should get you simple bypassing for XIPT for anyone who wants it.